Law enforcement sources tell us cops have been on the case since September. According to docs -- obtained by TMZ -- a woman sent a message on the Church of Scientology website saying, "I hate the United States Because I never get anything I want 100%. I hate President Obama, Hillary Clinton, Donald Trump, all Gerontologists ..."
She goes on ... "This is why I will gladly serve you to the satan ..."
Cops are not saying how serious it is, but they're calling it a death threat investigation. They've served a search warrant and believe they know the identity of the suspect, but she hasn't been arrested.